There are two basic methods of uncoiling a spool of wire: the tangential system whereby the wire is drawn off in a plane perpendicular to the axis of the spool, which is set up to pivot about its axis, and the axial system whereby the wire is drawn off from a point on the axis of the spool, which in this case is usually fixed in its support.
The axial uncoiling method is coming into wider and wider use, for two principal reasons. The first is a result of developments in cablemaking, in which spools of ever increasing size are being adopted, even for the finest of wires. Since the uncoiling speeds are being gradually raised, it is becoming more and more important to minimize the rotating masses.
The axial uncoiling method avoids this problem, in the sense that the spool is stationary. Within the uncoiling method, an arm is sometimes provided which pivots about the spool and is articulated about an axis corresponding to the spool axis. This arm, whose free extremity carries a roller to guide the wire, helps to prevent wire blockages, notably when the wire is level with the cheeks of the spool. The arm is kept rotating by the tension in the wire, but has the disadvantage of transmitting to the wire a higher tension than can be permitted at high uncoiling speeds.
One way of overcoming this disadvantage is to motorize the arm and regulate its speed as a function of the measured tension in each wire. Nevertheless, this is a costly expedient which is only acceptable for special applications.
For this reason it is becoming increasingly popular to dispense with the arm and draw the wire over a highly polished ring surrounding the spool cheek on the drawing side. This ring can be supplemented by a disc set with flexible radial bristles which hold the wire in check as it rotates round the ring.
Various systems can be used: a fixed ring and fixed-bristle disc; a spinning ring on a pivot coaxial with the spool axis and a fixed-bristle disc; or again a ring and bristled disc both spinning on a pivot coaxial with the spool axis.
To the extent that the ring can spin freely, it plays a role similar to that of the arm referred to previously in facilitating the uncoiling action. Nevertheless, if very high uncoiling speeds are sought, the tension is found to increase correspondingly and to vary during the process because as the end of the spool is approached, the speed at which the wire rotates is appreciably increased.
Finally, if the take-off machine suddenly stops, the ring continues to rotate and can take the wire with it, thereby causing loss of tension.